I How can objects even roll?

So in most of intro physics rolling questions, the masses are assumed to be rigid. So if I roll a sphere on frictional plane, it will move forward and the friction force will help stablize it until pure roll.

However, how can there even be a friction force assumed in these problems? The point of contact is one point of dimension 0. How can a friction force be exterted on this point? Also, even if it could be pushed. There is no point paralell to it to push it as all the points in the plane are constantly below it.

So in most of intro physics rolling questions, the masses are assumed to be rigid. So if I roll a sphere on frictional plane, it will move forward and the friction force will help stablize it until pure roll.

However, how can there even be a friction force assumed in these problems? The point of contact is one point of dimension 0. How can a friction force be exterted on this point? Also, even if it could be pushed. There is no point paralell to it to push it as all the points in the plane are constantly below it.

Theoretically a force can be applied at a single point. In practice, there will always be a small area of contact between the object and the surface.

Theoretically a force can be applied at a single point. In practice, there will always be a small area of contact between the object and the surface.

I don't follow your second question.

What I mean is that the ground can only exert a normal force up. It can't exert a force to the side. In sliding friction problems, the only way we can assume friction works is the microspicly, the surfaces are jagged.

I don't see how a side way force can be produced for rolling on a point. Unless, if we zoom in, finding the ball is more like a gear.

What I mean is that the ground can only exert a normal force up. It can't exert a force to the side. In sliding friction problems, the only way we can assume friction works is the microspicly, the surfaces are jagged.

I don't see how a side way force can be produced for rolling on a point. Unless, if we zoom in, finding the ball is more like a gear.

Again, theoretically a surface with friction can exert a tangential as well as a normal force. If you are asking about the nature of friction, then it must result from the sort of interaction you suggest. A snooker ball must be deforming the cloth to some extent.

That doesn't invalidate the simplified model, as long as the model produces accurate results.

What I mean is that the ground can only exert a normal force up. It can't exert a force to the side. In sliding friction problems, the only way we can assume friction works is the microspicly, the surfaces are jagged.

I don't see how a side way force can be produced for rolling on a point. Unless, if we zoom in, finding the ball is more like a gear.

As the contact area approaches zero the pressure increases towards infinity. So it's very hard to have a perfect zero area point contact. For example you need infinitely hard surfaces to avoid them distorting.

In short it's hard to avoid all friction in the situation you describe.